The Enhancer of split transcription factor Her8a is a novel dimerisation partner for Her3 that controls anterior hindbrain neurogenesis in zebrafish

Transcriptional Regulators with Broad Expression in the Zebrafish Spinal Cord

Background

The spinal cord is a crucial part of the vertebrate CNS, controlling movements and receiving and processing sensory information from the trunk and limbs. However, there is much we do not know about how this essential organ develops. Here, we describe expression of 21 transcription factors and one transcriptional regulator in zebrafish spinal cord.

Results

We analyzed the expression of aurkb, foxb1a, foxb1b, her8a, homeza, ivns1abpb, mybl2b, myt1a, nr2f1b, onecut1, sall1a, sall3a, sall3b, sall4, sox2, sox19b, sp8b, tsc22d1, wdhd1, zfhx3b, znf804a, and znf1032 in wild-type and MIB E3 ubiquitin protein ligase 1 zebrafish embryos. While all of these genes are broadly expressed in spinal cord, they have distinct expression patterns from one another. Some are predominantly expressed in progenitor domains, and others in subsets of post-mitotic cells. Given the conservation of spinal cord development, and the transcription factors and transcriptional regulators that orchestrate it, we expect that these genes will have similar spinal cord expression patterns in other vertebrates, including mammals and humans.

Conclusions

Our data identify 22 different transcriptional regulators that are strong candidates for playing different roles in spinal cord development. For several of these genes, this is the first published description of their spinal cord expression.

Genome-wide identification and characterization of bHLH family genes from orchardgrass and the functional characterization of DgbHLH46 and DgbHLH128 in drought and salt tolerance

Basic helix-loop-helix (bHLH) is the second largest family of transcription factors that widely exist in plants and animals, and plays a key role in a variety of biological processes. As an important forage crop worldwide, little information is available about the bHLH family in orchardgrass (Dactylis glomerata L.), although a huge number of bHLH family have been identified and characterized in plants. In this study, we performed genome-wide analysis of bHLH transcription factor family of orchardgrass and identified 132 DgbHLH genes. The phylogenetic tree was constructed by using bHLH proteins of orchardgrass, with Arabidopsis thaliana and Oryza sativa bHLH proteins, to elucidate their homology and classify them into 22 subfamilies. The results of conserved motifs and gene structure support the classification of DgbHLH family. In addition, chromosomal location and gene duplication events of DgbHLH genes were further studied. Transcriptome data exhibited that DgbHLH genes were differentially expressed in different tissues of orchardgrass. We analyzed the gene expression level of 12 DgbHLH genes in orchardgrass under three types of abiotic stresses (heat, salt, and drought). Finally, heterologous expression assays in yeast indicated that DgbHLH46 and DgbHLH128 may enhance the resistance to drought and salt stress. Furthermore, DgbHLH128 may also be involved in abiotic stress by binding to the MYC element. Our study provides a comprehensive assessment of DgbHLH family of orchardgrass, revealing new insights for enhancing gene utilization and improving forage performance.

An Update on the Molecular Mechanism of the Vertebrate Isthmic Organizer Development in the Context of the Neuromeric Model

A crucial event during the development of the central nervous system (CNS) is the early subdivision of the neural tube along its anterior-to-posterior axis to form neuromeres, morphogenetic units separated by transversal constrictions and programed for particular genetic cascades. The narrower portions observed in the developing neural tube are responsible for relevant cellular and molecular processes, such as clonal restrictions, expression of specific regulatory genes, and differential fate specification, as well as inductive activities. In this developmental context, the gradual formation of the midbrain-hindbrain (MH) constriction has been an excellent model to study the specification of two major subdivisions of the CNS containing the mesencephalic and isthmo-cerebellar primordia. This MH boundary is coincident with the common Otx2-(midbrain)/Gbx2-(hindbrain) expressing border. The early interactions between these two pre-specified areas confer positional identities and induce the generation of specific diffusible morphogenes at this interface, in particular FGF8 and WNT1. These signaling pathways are responsible for the gradual histogenetic specifications and cellular identity acquisitions with in the MH domain. This review is focused on the cellular and molecular mechanisms involved in the specification of the midbrain/hindbrain territory and the formation of the isthmic organizer. Emphasis will be placed on the chick/quail chimeric experiments leading to the acquisition of the first fate mapping and experimental data to, in this way, better understand pioneering morphological studies and innovative gain/loss-of-function analysis.

The BMP signaling gradient is interpreted through concentration thresholds in dorsal-ventral axial patterning

Bone Morphogenetic Protein (BMP) patterns the dorsal–ventral (DV) embryonic axis in all vertebrates, but it is unknown how cells along the DV axis interpret and translate the gradient of BMP signaling into differential gene activation that will give rise to distinct cell fates. To determine the mechanism of BMP morphogen interpretation in the zebrafish gastrula, we identified 57 genes that are directly activated by BMP signaling. By using Seurat analysis of single-cell RNA sequencing (scRNA-seq) data, we found that these genes are expressed in at least 3 distinct DV domains of the embryo. We distinguished between 3 models of BMP signal interpretation in which cells activate distinct gene expression through interpretation of thresholds of (1) the BMP signaling gradient slope; (2) the BMP signal duration; or (3) the level of BMP signal activation. We tested these 3 models using quantitative measurements of phosphorylated Smad5 (pSmad5) and by examining the spatial relationship between BMP signaling and activation of different target genes at single-cell resolution across the embryo. We found that BMP signaling gradient slope or BMP exposure duration did not account for the differential target gene expression domains. Instead, we show that cells respond to 3 distinct levels of BMP signaling activity to activate and position target gene expression. Together, we demonstrate that distinct pSmad5 threshold levels activate spatially distinct target genes to pattern the DV axis.

This study tested three models of how a BMP morphogen gradient is translated into differential gene activation that specifies distinct cell fates, finding that BMP signal concentration thresholds, not gradient shape or signal duration, position three distinct gene activation domains.

HLH-29 regulates ovulation in C. elegans by targeting genes in the inositol triphosphate signaling pathway

The reproductive cycle in the nematode Caenorhabditis elegans depends in part on the ability of the mature oocyte to ovulate into the spermatheca, fuse with the sperm during fertilization, and then exit the spermatheca as a fertilized egg. This cycle requires the integration of signals between the germ cells and the somatic gonad and relies heavily on the precise control of inositol 1,4,5 triphosphate (IP₃)levels. The HLH-29 protein, one of five Hairy/Enhancer of Split (HES) homologs in C. elegans, was previously shown to affect development of the somatic gonad. Here we show that HLH-29 expression in the adult spermatheca is strongly localized to the distal spermatheca valve and to the spermatheca-uterine valve, and that loss of hlh-29 activity interferes with oocyte entry into and egg exit from the spermatheca. We show that HLH-29 can regulate the transcriptional activity of the IP₃ signaling pathway genes ppk-1, ipp-5, and plc-1 and provide evidence that hlh-29 acts in a genetic pathway with each of these genes. We propose that the HES-like protein HLH-29 acts in the spermatheca of larval and adult animals to effectively increase IP₃ levels during the reproductive cycle.